This invention relates to a method and apparatus for determining the presence of volatile inorganic compounds in the environment. More specifically this invention relates to a method and apparatus for determining the presence and concentration of organoarsenicals, including Lewisite, in ambient air in near-real-time.
Lewisite collectively refers to Lewisite I, dichloro (2-chlorovinyl) arsine, C.sub.2 H.sub.2 AsCl.sub.3, and its analogs Lewisite II, bis (2-chlorovinyl) chloroarsine, (C.sub.2 H.sub.2 Cl).sub.2 AsCl, and Lewisite III, (C.sub.2 H.sub.2 Cl).sub.3 As. Lewisite was developed during World War I as a chemical warfare agent. Several countries produced large quantities of the agent before, during and after World War II. The Chemical Weapons Convention treaty, recently signed, requires the destruction of Lewisite. In implementing the Chemical Weapons Convention treaty, it will be necessary to monitor the facilities at which various chemical agents including Lewisite may be stored for compliance with the agreement. The inspection procedures must meet stringent standards for safety, quality assurance and accountability. In preparing for these inspections a technology gap has been identified in the ability to detect and monitor for the presence of Lewisite in ambient air, particularly in the facilities where chemical warfare agents are stored.
Prior methods for monitoring the presence of trace levels of Lewisite in ambient air are based on sampling using liquid impingers or polymeric reactors and detection based on atomic absorption spectroscopy, ion chromatography, or gas chromatography. One of these prior methods uses the collection of Lewisite in a caustic-containing liquid impinger. The caustic solution in the impinger will decompose the Lewisite (using Lewisite I as an example) as shown in the following reaction mechanism: EQU C.sub.2 H.sub.2 AsCl.sub.3 +6OH.sup.- .revreaction.C.sub.2 H.sub.2 +AsO.sub.3.sup.3- +3Cl.sup.- +3H.sub.2 O
Acetylene that is produced when the Lewisite is decomposed by the hydroxide ion is measured by gas chromatography. This method is susceptible to interferences as well as the difficulty of quantitatively recovering the acteylene.
Two other methods, atomic absorption spectroscopy or ion chromatography, use this same type of sampling approach to measure the arsenite ion produced upon base hydrolysis. These methods require large and complex hardware and are thus suitable for the laboratory and are not portable so that they can be used at field sites.
Another prior method uses the reaction of Lewisite with 1,3-propanedithiol (or similar compounds) in a polymeric (e.g., polyester) reactor to convert Lewisite to a stable complex that can be analyzed by gas chromatography. However, this method is slow, insensitive, and imprecise.